A solid polymer electrolyte with a poly (vinyl-alcohol) (PVA) matrix and a mixture of H3PW12O40 (PWA) and H4SiW12O40 (SiWA) as proton conductor was developed. The proton conductivity of this polymer electrolyte reached 0.013 scm(-1) at room temperature with a very low activation energy of 3.9 kJ mol(-1) at its optimal ratio (when SiWA and PWA were mixed in equal proportions). The room temperature proton conductivity was higher than that of pure PVA-PWA or PVA-SiWA electrolytes. The solid polymer electrolyte also showed good stability over time and at varying levels of relative humidity. A pseudocapacitor using this solid polymer electrolyte was demonstrated and showed good high rate performance and cycle life. (C) 2010 Elsevier B.V. All rights reserved.